Investigations of hydrology and hydrochemistry of remote river basins are hampered by the lack of discharge and chemistry data. In large basins, a further issue is unraveling landscape and other controls on solute loads. This study uses tributary basin characteristics and point samples of solute chemistry to assess spatial patterns in annual solute yields.

First we show that annual discharge of the Yukon River can be computed by summing calculated annual discharges from 42 predominantly ungaged tributaries (Fig. 1). Annual discharge is calculated from basin area and average annual precipitation specific to that area using the regionalization of streamflow statistics method [1]. The success of this calculation shows that groundwater, ET, and storage are generally integrated throughout the basin. We estimate a total annual discharge for the Yukon River of 211 km^3 yr^-1 which compares favorably to the instrument record.

Next, annual loads for 11 solutes are determined by combining annual discharge with point measurements of solute concentrations. The summed contributions of tributary waters show that the Yukon River discharges approximately 33x10^12g of dissolved solids each year at Pilot Station. The solutes are dominated by cations calcium and magnesium (5.66x10^12 and 1.42x10^12g yr^-1) and anions bicarbonate and sulfate (17.2x10^12 and 5.42x10^12g yr^-1). These calculated loads compare well with loads calculated using the LOADEST computer program [2] based on daily discharge and 34 instantaneous solute concentration measurements made at the USGS gage near the Yukon River mouth (Fig. 2). Calculated loads were also compared with LOADEST loads at two other stations along the mainstem of the Yukon showing an average difference of 9% for all solutes.

These findings show that annual solute yields for a major subarctic river can be determined from tributary basins using calculated discharges and distributed point measurements of solute concentration. This work provides the basis for analyzing the spatial controls on solute yields within the Yukon River basin, such as the distribution of rock types, permafrost, vegetation zones, and tributary size.

Fig 1. Calculated and measured average annual discharge (QA) for the Yukon River. Distance in km along the bottom axis is length of river course from the outlet of Atlin Lake, BC (source). Black bars indicate individual tributary discharge and the thick grey line is cumulative discharge. X’s mark measured QA for each year of study at the three ﬁxed station sites near Eagle, Stevens Village, and Pilot Station, Alaska. "Error" bars show the minimum and maximum QA measured at those sites over the entire instrument record: 56, 29, and 26 years respectively.

Fig 2. Comparison between selected solute loads determined by summing tributary inputs (Closed symbols, dotted line) and LOADEST computer program calculations (open symbols and solid line) at three locations along the Yukon River. Tributary loads are average annual and those calculated by LOADEST are average annual for water years 2001 through 2005.